Plastic containers are commonly used for packaging items in a wide range of fields, including food and beverage, medicine, health and beauty, and home products. Plastic containers are known for being easily molded, cost competitive, lightweight, and generally suitable for many applications.
Because plastic containers may permit low molecular gases, such as oxygen and carbon dioxide, to slowly permeate through their physical configurations, the use of plastic containers sometimes proves to be less desirable when compared to containers formed from other less permeable materials, such as metal or glass. In most applications, the shelf life of the product contents is directly related to the package's ability to effectively address such molecular permeation. In the case of carbonated beverages, such as beer, oxygen in the atmosphere surrounding the container can gradually permeate inwardly through the plastic walls of the container to reach inside of the container and deteriorate the contents. Likewise, carbon dioxide gas associated with the contents may permeate outwardly through the plastic walls of the container until eventually being released on the outside, causing the carbonated beverage to lose some of its flavor and possibly become “flat”.
To address some of the foregoing concerns, plastic container manufacturers have utilized various techniques to reduce or eliminate the absorption and/or permeability of such gases. Some of the more common techniques include: increasing the thickness of all or portions of the walls of the container; incorporating one or more barrier layers into the wall structure; including oxygen-scavenging or reacting materials within the walls of the containers; and applying various coatings to the internal and/or external surface of the container. However, conventional barrier and/or scavenger materials will frequently not effectively curtail the permeation of both oxygen and carbon dioxide over extended periods of time.
It is preferred to have a plastic container with high barrier properties to prevent oxygen ingress and carbonation egress from occurring. Barrier treatment on the internal surface of the plastic container, as for example, carbon treatment, prevents most oxygen from entering the container. A typical 16 oz. carbon coated plastic container has oxygen ingress of from 0.0010 to 0.0060 cc/package/day. This is a high barrier compared to a typical untreated polyethylene terephthalate (PET) container which is typically in the range of 0.0400 to 0.0600 cc/package/day.
However, in some circumstances it is desirable to have less than the 0.0010 to 0.0060 cc/package/day oxygen ingress and for these applications an oxygen scavenger may be used in the plastic structure in combination with the barrier treatment. For example, the structure may consist of an oxygen scavenger in a mono-layer plastic structure with a carbon coating on the inside surface. This will allow the container to reduce the oxygen ingress to less than 0.0010 to 0.0060 cc/package/day through the container sidewall. However, disadvantageously the closure will typically allow more oxygen to permeate through into the container than is desirable. A barrier on the internal surface of the container will prevent the scavenger from scavenging oxygen which comes through the closure.
Therefore, a need exists and it is an object of the present invention to provide an improved plastic container including oxygen scavenging materials and barrier materials suitable for holding products, such as carbonated beverages or other food products, and having a long shelf life.
It is a further object of the present invention to provide an improved plastic container as aforesaid which overcomes the problem of oxygen ingress through the container.
Further objects and advantages of the present invention will appear hereinbelow.